1. Field of the Invention
The present invention relates to a display device whose luminance is controllable in accordance with a current quantity applied to a display element, or a light emitting time period. More particularly, it relates to a display device which is configured of display elements represented by an emissive type, also termed “organic EL (ElectroLuminescence) or organic light emitting diodes”.
2. Description of the Related Art
Owing to the spread of various information processors, there are various display devices complying with roles. Among them, a display employing organic EL elements (an organic EL display device) has been highlighted as a display device of emissive type. An OLED or the like light emitting element for use in the display device does not require backlight as in a liquid-crystal display (liquid-crystal display device), and it is suited to a lower power consumption. Moreover, as compared with the liquid-crystal display, the organic EL element has merits such as a higher pixel visibility and a higher response rate.
Further, the organic EL element has characteristics similar to those of a diode, and its luminance can be controlled by a current quantity which is caused to flow through the element. Driving methods in such an emissive type display device are disclosed in JP-A-2006-91709, etc. Besides, regarding a configuration in which a touch panel or the like input device is incorporated into such a display device, JP-A-10-49305, etc. can be mentioned.
As the characteristic of the organic EL element (OLED), the internal resistance value of the element changes, depending upon a service period or an ambient environment. Especially, the organic EL element has the property that, when the service period increases, the internal resistance heightens secularly, so a current to flow through the element decreases. Therefore, when the pixels of an identical place within a screen, for example, a menu display are lit up for a long time, an burn-in phenomenon occurs in the place. For coping with the burn-in phenomenon, the state of the pixel needs to be detected. A method for the detection is one in which the pixel state is detected in the blanking period of display data. In the blanking period, the pixel is not caused to emit light, and hence, a displaying voltage is not applied. Therefore, using a power source separate from a power source for the light emission, a certain fixed current is applied to the pixel in the blanking period, and a voltage in this state is detected, whereby a degradation in the burn-in is detected from the change of the voltage. Besides, since the current cannot be applied to the pixel during a display period, a circuit for the above detection is used only in the blanking period.
Meanwhile, in order to detect a temperature characteristic and an ambient brightness and to detect a touch panel or the like input sensor used, similar detection circuits are respectively necessitated. In furnishing the system of the display device with the detection circuits, further controllers or the like control means are necessitated for coping with the burn-in detection, the temperature characteristic detection and the ambient brightness detection, and a circuit scale becomes large.